Roller threaded spindle with nut

ABSTRACT

A threaded spindle which transmits axial thrust to a nut disposed for a relative rotation thereon, through rollers, the nut having an endless raceway of zero pitch around its inner periphery with the rollers disposed for simultaneous engagement with opposing flanks of the raceway and the screw thread to transmit axial thrust resulting from relative rotation of the screw and nut, the raceway being in the shape of an Archimedean spiral having sufficient clearance at diametrically opposed locations on opposite sides of the screw for the rollers to disengage from and move axially across the crest of the thread of the screw incident to their movement around the raceway.

United States Patent [1 1 Orend 451 Sept.18, 1973 ROLLER THREADEDSPINDLE WITH NUT [21] Appl. No.: 120,920

[30] Foreign Application Priority Data FOREIGN PATENTS OR APPLICATIONS11/1954 ltaly 74/424.8 R

Primary Examiner--C. .1. Husar Attorney-Watson, Cole, Grindle & Watson[57] ABSTRACT A threaded spindle which transmits axial thrust to a nutdisposed for a relative rotation thereon, through rollers, the nuthaving an endless raceway of zero pitch around its inner periphery withthe rollers disposed for simultaneous engagement with opposing flanks ofthe raceway and the screw thread to transmit axial thrust resulting fromrelative rotation of the screw and nut, the raceway being in the shapeof an Archimedean spiral having sufficient clearance at diametricallyopposed locations on opposite sides of the screw for the rollers todisengage from and move axially across the crest of the thread of thescrew incident to their movement around the raceway.

12 Claims, 6 Drawing Figures ROLLER THREADED SPINDLE WITH NUT Rollerthreaded spindles have become known under the name of ball revolvingspindle. Such spindles are described in the U.S. Pat. Nos. 3,056,331 1and 3,156,133. These known roller threaded spindles have the drawbackthat, through the use of balls, only a point contact takes place at theflanks of the nut and threaded spindle. Besides that, the manufacture,particularly the grinding of the nut after hardening, is very difficultand thus production is very expensive. An other difficulty is thegeometric shape of the profile track which is composed of two elipticarches.

In thecase of the design according to French Pat. No. 1,399,664,cylindrical rollers are used in place of balls, which permit a higherload of the threaded spindle as well as of the nut through a linecontact between rollers and flank; in this case, however, the necessityof areturn channel for the rollers is. disadvantageous. The geometricshape of the thread (profile track) in the case of this design isrelatively simple. Even in this case, as in the case of all nuts knownup to this time, the main difficulties in the manufacture of the nut hasnot been solved, which consists in that in a relatively small bore itisnecessary to tool a number of threads of the highest surface quality andprecision of shape. Besides, the nut-due to the return channel for therollers--must be built with a very large diameter. But precisely inregard to the dimensions, there are quite considerable requirements fora roller threaded spindle in machine tool construction and particularlyin the case of steering mechanisms in the construction of motorvehicles.

It is an object of the invention to create a roller threaded spindlewhich will guarantee a high precision of leadhaving simple manufacturingmethods, complete freedom of play and great efficiency. The rollerthreaded spindle iscapable of being built quite compactly for use ininstallations where but minimum space is available.

According to the invention, this will be achieved through the fact thatthe radially variable thread is determined in its shape by anArchimedean spiral. As a result of that, one will achieve even in thecase of use of cylindrical roll bodies, which perform line contact withthe cooperating threads and therefore are capable of absorbing higherloads, constant contact between the threaded spindle and the nut. Areturn channel for the roll bodies becomes superfluous.

It is particularly advantageous to make the thread radially and axiallyvariable. That is to say, the thread is made at the same time radiallyand axially rising and declining or else rising or declining in adisplaced manner. The Archimedean spiral may be repeated correspondingto the number of threads.

In a further development of the invention, the nut has been subdividedinto at least two nut partsor segments and each of these segmentscontains a thread or, in the ple. The halves of the nut can be producedfor example by way of a compression flow processLA high degree ofprecision of the lead can be achieved. Through the use of cylindricalroll bodies in connection with the Archimedean spiral and the divisionof the nut, it is possible to construct a very compact roller threadedspindle with the greatest precision and reliability.

It is also possible to use instead of cylindrical roll bodies, rollbodies with a conic, convex or spherical shape with correspondingdevelopment of the thread and of. the threaded spindle or lead screw.

As a result of the crossing rotational axes of the roll bodies orrollers and the development of the thread in the shape of an Archimedeanspiral, high radial and axial forces can be absorbed by a compactarrangement. A return channel for the roll bodies is not necessary.

The preferred embodiment of the invention will be explainedin moredetail in the following description, in conjunction with theaccompanying drawing, in which:

FIG. 1 is a perspective view of the nut produced in half sections inaccordance with the present invention showing the interior of eachsection spaced apart for clarity and showing a typical roll body withinthe racey;

FIG. 2 is a plan perspective view of one of two identical half-sectionsshowing the interior thereof; and

FIGS. 3 to 6 are sectional views taken along the lines 3-3 to 6-6 ofFIG. 1, respectively, of the nut in its various relationships to thethreads of a spindle.

Halves or segments 2 of a nut run on a two-start threaded spindle l,which enclose between them cylindrical roll bodies 3 with crossing axesof rotation and which are held together by a ring 4. Instead of thecylindrical roll bodies 3, one can also use roll bodies with a conic,convex or spherical shape with corresponding development of the threadand the threaded spindle. A radially and at the same time axiallyvariable development of the profile of the thread or raceway 7 of thenut is also particularly favorable (as shown in the drawing), whereby itis also possible to develop it with zero pitch radially rising anddeclining. As a result of that, the loading capacity will be greatlyincreased.

FIGS. 1 and 2 each show the thread of'raceway 7 of the nut correspondingto the shape of an Archimedean spiral in each half or segment 2 of thenut, increasing in radius from A to E and decreasing in radius from E toB.

In FIG. 3, a section through the threaded spindle l and the nut has beenshown along the line 3-3 of FIG. 2 A ring 4 holds the nut halves 2together. At least two such halves or segments 2 constitute the nut, andthese together with the roll bodies or rollers 3 and the threadedspindle or lead screw 1 constitute the roller threaded spindle. On eachof the two nut halves 2, a bridge or retainer flange 5 has been providedto retain the roll bodies 3 in the raceway 7.

As a result of that, it is possible to put together assembly elementsfrom halves of partial nuts closed with roll bodies, which correspondingto the pertinent load, are put together from two, four, six or even morepartial nuts and which are inserted without play on the threaded spindlethrough axial tension. Naturally, it is possible to use merely a singlenut consisting of two nut halves of a partial nut held together by ring4 as in the drawing for use in the case of small loads.

FIG. 4 is a cross-section taken along line 4-4 of FIG. 2, indicating howat this location, roll bodies 3 have moved radially outwardly from theroot circle of the screw thread without being displaced axially from theraceway 7 of the nut, which raceway has zero pitch.

In FIG. 5, it will be seen that the roll bodies 3 are located by theretainer flange or bridge 5 out of contact with the screw thread whilemoving axially across its crest. From the largest diameter of theArchimedean spiral (FIG. 4), the rollers or roll bodies 3 roll from theaddendum circle via the root circle to a point, shown in section 4-4, onthe opposite flank of the bridge of the threaded spindle 1, as shown insection 6-6 in FIG. 6.

The rollers 3 guided by the nut 2 unroll along the flanks of the raceway7 in such a way-corresponding to the lead-that the roll bodies unrollfrom the root circle of the profile of the threaded spindle, via theaddendum circle on the opposite flank of the thread bridge again to theroot circle. That is to say, the roll bodies rise around the axial leadpath of the threaded spindle in the nut radially to the largest diameterof the Archimedean spiral, and then unroll on the opposite flank of thebridge to the root circle of the threaded spindle. A nut with a purelyradial lead is to be used both for the right-hand rising and left-handrising threaded spindle in the same way, whereby it is irrelevantwhether there is employed a one-threaded or multiple threaded spindle.

Thus, on their return path, the roll bodies or rollers function tosupport the nut against tilting on the screw.

It will thus be seen that the spindle or lead screw 1 is of circularcross-section with an external thread 6 of given pitch thereon. The nut2 which is disposed for relative rotation in telescoping relation on thescrew is formed around its inner periphery with an endless raceway 7 ofzero pitch with the plurality of rollers 3 (only one of which is shownin FIG. 1 for clarity) operatively disposed in the raceway for movementtherearound. It will be particularly noted that the thread 6 and theraceway 7 are each of substantial V-shape in crosssection, having itsopposite flanks at right angles to each other, the opposite flanks ofeach thread respectively being parallel to the opposite flanks of theraceway. Further, it will be noted that each roller 3 is of cylindricalconfiguration with opposite axial end faces at right angles to itscylindrical surface, or in other words, disposed normally to itscylindrical axis. At least some of the rollers 3 are arranged with thecylindrical surface of each in simultaneous rolling engagement with aflank of the screw thread 6 and an opposing parallel flank of theraceway 7, while others of the rollers have their opposite axial endfaces in simultaneous abutting engagement with another flank of thescrew thread and another relatively parallel flank of the raceway 7. Itwill be further noted that the raceway is in the form of an Archimedeanspiral as is best illustrated in FIG. I, having its maximum diameter inthe plane 5-5 of FIG. 2. At the diametrically opposed locations 55 inFIG. 1, the race way has sufficient clearance with the screw thread 6that the rollers, as they move outwardly on the flank of thescrew-thread in approaching the locations E and F will move completelyoff of the thread flank to become completely disengaged from the thread6, as indicated in FIG. 5, and thereafter to move radially inwardly intoengagement with the opposite flank of the thread during their continuedmovement through and past the points or locations E and F, respectively.

It will thus be apparent that the rollers will be operative to transmitan axial thrust between the lead thread and the nut at all locationsaround the circumference of the lead screw except at and adjacent themaximum diameter locations E, F of the raceway, where the rollers aretemporarily disengaged from the lead screw during their transitionalmovement across the thread crest from one flank of the thread to theother.

In this application, there is shown and described only the preferredembodiment of the invention, simply by way of illustration of thepractice of the invention, though it is to be recognized that theinvention is capable of other and different embodiments and that itsdetails may be changed in various ways without departing from the scopeof the invention as defined in the appended claims.

Having thus described my invention, I claim:

1. A roller threaded spindle with a nut, roll bodies guided by said nut,said nut being provided with a raceway of zero pitch which at firstincreases radially and then diminishes radially, in which the rollbodies maintain a constant contact with the threaded spindle and thenut, characterized in that the radially variable raceway is in the formof an Archimedean spiral.

2. A roller threaded spindle according to claim 3, characterized in thatthe thread is radially and axially variable.

3. A roller threaded spindle according to claim 1, characterized in thatthe Archimedean spiral is repeated corresponding to the number ofthreads.

4. A roller threaded spindle according to claim 1, characterized in thatthe nut is formed of two identical half sections, and in that one ofthese sections defines a part of said raceway.

5. A roller threaded spindle according to claim 4, characterized in thatthe nut sections are divided along a plane of symmetry normal to therotational axis of said nut.

6. A roller threaded spindle according to claim 4, characterized in thatbridges on the nut sections enclose the roll bodies in the manner of acage.

7. A roller threaded spindle according to claim 4, characterized in thatthe nut sections are held together by a ring.

8. A roller threaded spindle according to claim 7, characterized in thatthe nut constitutes a rigid unit free of axial and radial play betweenthe respective nut sections.

9. The combination of a lead screw of circular crosssection, having athread of given pitch thereon, a relatively rotatable nut in telescopingrelation on the screw, the nut having an endless raceway of zero pitcharound its inner periphery; and a plurality of rollers operativelydisposed in said raceway for movement therearound to transmit an axialthrust between said screw and said nut; the improvements wherein saidthread being V- shaped in a cross-section, said thread and said racewayhaving opposite flanks at right angles to each other; each said rollerbeing of cylindrical configuration with opposite axial end faces atright angles to its cylindrical surface, at least some of said rollershaving their cylindrical surfaces in simultaneous rolling engagementwith a flank of said screw thread and a flank of said raceway; andothers of said rollers having their opposite axial end faces insimultaneous engagement with the flank of nut has a correspondingplurality of said raceways.

12. The combination defined in claim 9, in which said nut is ofcomposite construction, comprising a pair of separate segments disposedsymmetrically to each other on opposite sides of a plane of symmetrywhich extends normally to the axis of relative rotation of said screwand said nut, the said segments respectively being formed to define therelatively opposing flanks of said raceway, and means for securing saidsegments in their symmetrical relationship.

1. A roller threaded spindle with a nut, roll bodies guided by said nut,said nut being provided with a raceway of zero pitch which at firstincreases radially and then diminishes radially, in which the rollbodies maintain a constant contact with the threaded spindle and thenut, characterized in that the radially variable raceway is in the formof an Archimedean spiral.
 2. A roller threaded spindle according toclaim 1, characterized in that the thread is radially and axiallyvariable.
 3. A roller threaded spindle according to claim 1,characterized in that the Archimedean spiral is repeated correspondingto the number of threads.
 4. A roller threaded spindle according toclaim 1, characterized in that the nut is formed of two identical halfsections, and in that one of these sections defines a part of saidraceway.
 5. A roller threaded spindle according to claim 4,characterized in that the nut sections are divided along a plane ofsymmetry normal to the rotational axis of said nut.
 6. A roller threadedspindle according to claim 4, characterized in that bridges on the nutsections enclose the roll bodies in the manner of a cage.
 7. A rollerthreaded spindle according to claim 4, characterized in that the nutsections are held together by a ring.
 8. A roller threaded spindleaccording to claim 7, characterized in that the nut constitutes a rigidunit free of axial and radial play between the respective nut sections.9. The combination of a lead screw of circular cross-section, having athread of given pitch thereon, a relatively rotatable nut in telescopingrelation on the screw, the nut having an endless raceway of zero pitcharound its inner periphery; and a plurality of rollers operativelydisposed in said raceway for movement therearound to transmit an axialthrust between said screw and said nut; the improvements wherein saidthread being V-shaped in a cross-section, said thread and said racewayhaving opposite flanks at right angles to each other; each said rollerbeing of cylindrical configuration with opposite axial end faces atright angles to its cylindrical surface, at least some of said rollershaving their cylindrical surfaces in simultaneous rolling engagementwith a flank of said screw thread and a flank of said raceway; andothers of said rollers having their opposite axial end faces insimultaneous engagement with the flank of said screw thread and a flankof said raceway; said raceway being in the shape of an Archimedeanspiral proportioned to leave sufficient clearance with the lead screw atdiametrically opposed locations for the rollers to disengage from andmove axially across the crest of the screw thread.
 10. The combinationdefined in claim 9 in which said nut includes retainer flanges overlyingsaid raceway adjacent said diametrically opposed locations to retain therollers in said raceway.
 11. The combination defined in claim 10, inwhich the lead screw has a plurality of said threads and the nut has acorresponding plurality of said raceways.
 12. The combination defined inclaim 9, in which said nut is of composite construction, comprising apair of separate segments disposed symmEtrically to each other onopposite sides of a plane of symmetry which extends normally to the axisof relative rotation of said screw and said nut, the said segmentsrespectively being formed to define the relatively opposing flanks ofsaid raceway, and means for securing said segments in their symmetricalrelationship.